1. Field of the Invention
The invention relates to an injector for a fuel injection system for internal combustion engines, having a housing, having a nozzle needle, having a control chamber, and having a pressure chamber, defined by a pressure shoulder of the nozzle needle; the control chamber is defined at least indirectly by the nozzle needle, and the control chamber communicates hydraulically with a fuel inlet via an inlet throttle, and the control chamber can be made to communicate hydraulically by means of a control valve with a fuel return via an outlet throttle.
Injectors of the above type with pressure-controlled or stroke-controlled nozzle needles are known from the prior art.
2. Object and Summary of the Invention
The object of the invention is to further improve an injector for a fuel injection system for internal combustion engines in terms of its injection performance.
According to the invention, this object is attained by an injector for a fuel injection system for internal combustion engines, having a housing, having a nozzle needle, having a control chamber, and having a pressure chamber, defined by a pressure shoulder of the nozzle needle, wherein the control chamber is defined at least indirectly by the nozzle needle, and the control chamber communicates hydraulically with a fuel inlet via an inlet throttle, and wherein the control chamber can be made to communicate hydraulically by means of a control valve with a fuel return via an outlet throttle, in that a 3/2-way valve with a valve member is present; that the 3/2-way valve, in a first switching position, connects the pressure chamber and the fuel return hydraulically to one another; that in a second switching position, the 3/2-way valve connects the pressure chamber and the fuel inlet hydraulically to one another; and that the 3/2-way valve assumes the first or the second switching position as a function of the pressure difference between the fuel inlet and the control chamber.
In the injector of the invention, the nozzle needle opens under pressure control and is compulsorily closed when the pressure in the control chamber increases as a consequence of the closure of the control valve. By these provisions, the opening and closing of the nozzles can be varied independently of one another, within certain limits. Moreover, because of the compulsory closure of the nozzle needle, a rapid closure and suitability of the injector of the invention for performing both preinjections and postinjections as well are obtained.
In a variant of the invention, it is provided that the control chamber is embodied in two parts; that a first part of the control chamber is embodied in the nozzle needle; that a second part of the control chamber is embodied in the valve member; that the first part of the control chamber can be defined by a first shoulder in the housing; and that the second part of the control chamber is defined by a second shoulder in the housing. In this variant, the volume of the control chamber can be kept quite small, because the first part and second part of the control chamber are not triggered simultaneously but instead at staggered times. The result is a further improvement in the opening and in particular the closing performance of the injector of the invention. In a further feature of the invention, it is provided that the second part of the control chamber communicates hydraulically with the fuel inlet via an inlet throttle, and/or that the first part and the second part of the control chamber can be made to communicate with the fuel return, each via a respective outlet throttle, and/or that the first part and the second part of the control chamber communicate hydraulically with one another. In these refinements according to the invention, the volume of the control chamber can be reduced still further, and moreover it is assured that both parts of the control chamber can be supplied with fuel from the fuel return via the inlet throttle.
In a further supplement to the invention, it is provided that the 3/2-way valve has a valve member; that the control chamber is defined by one end face of the valve member; that the fuel inlet can be disconnected from the pressure chamber and/or the leak fuel return by a sealing seat that is embodied in the housing and cooperating with a sealing cone of the valve member; and that the diameter of the sealing seat is less than the diameter of the end face of the valve member.
As a result of the embodiment of the 3/2-way valve with at least one sealing seat, it can be assured that the fuel return and pressure chamber can be disconnected from one another without leakage. Moreover, the valve member, because of the difference in diameter of the sealing seat and the end face of the valve member, can be opened in a simple way as a function of the pressure difference between the fuel inlet and the control chamber.
In another feature of the invention, in the housing, a control edge cooperating with a portion, embodied as a valve piston, of the valve member is provided, and the hydraulic communication between the pressure chamber and the fuel return is controlled via the control edge, so that the advantages of a slide valve come into play in the second switching position of the injector of the invention.
To make production easier, it can be provided that a pressure rod is provided between the control chamber and the nozzle needle; and that the control chamber is defined by a first face end of the pressure rod; and that a second face end of the pressure rod rests on one face end of the nozzle needle. In this embodiment, there is hydraulically no difference from a one-part nozzle needle that directly defines the control chamber. However, it can also be advantageous, as already noted, for reasons of space, production or mounting, to provide a pressure rod between the control chamber and the nozzle needle.
Alternatively, the first part of the control chamber can be disposed in a pressure rod.
In a further feature of the invention, between the housing and the nozzle needle a nozzle spring is provided; and the nozzle spring presses the nozzle needle in the direction of a nozzle needle seat, so that the injector is closed when there is no pressure in the fuel inlet.
In another feature of the invention, between the housing and the valve member, a closing spring is provided, which presses the valve member in the direction of the sealing seat, so that the 3/2-way valve likewise assumes a defined position if the injector is without pressure.
Alternatively, the control valve can be actuated by an electromagnet or a piezoelectric actuator.
To simplify production and assembly, the housing can be embodied in two parts.
By using the injector of the invention in a common rail fuel injection system, the advantages of the invention can be made useful for these fuel injection systems as well.